Cephaleuros Kunze ex E.M.Fries, 1832

Lectotype species: Cephaleuros virescens Kunze ex E.M.Fries

Original publication: Fries, E.[M.] (1832). Systema mycologicum: sistens fungorum ordines, genera et species, huc usque cognitas, quas ad normam methodi naturalis determinavit / disposuit atque descripsit. Volumen III et ultimum. pp. [261]-524, [1]-202 p. ["Index alphabeticus generum, ..."]. Grypiswaldae: Sumptibus Entestii Mauritii.

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Description: Heterotrichous with filamentous to pseudoparenchymatous prostrate thallus and erect multicellular sterile or zoosporangia-bearing branches. Rhizoidal branches produced ventrally. Often forming orange to orange-red (due to cytoplasmic accumulations of carotenoids), velvet-like spots 10 mm or more in diameter. Branching dichotomous to pinnate, producing suborbicular thalli. Chloroplasts irregular parietal networks without pyrenoids. Nucleus single in vegetative cells. Central portion of intercellular cross walls with simple plasmodesmata. Structurally specialized cross walls between pedicel and zoosporangium with plasmodesmata located in central ring of thickened wall material.

Asexual reproduction by zoospores produced on fertile branches forming enlarged pyriform "head cells" producing, in turn, "sporangiate laterals" comprising short suffultory cell (or, neck cell, hook cell, stalk cell, pedicel, etc.) that bears an enlarged, ovoid zoosporangium (="Hackensporangium," ca. 21-36 m x 18-26 m) that abscises from suffultory cell by circumscissile tearing of outer wall and splitting of modified cross wall. Nipple-like protuberances from center of cross wall of both zoosporangium and suffultory cell may facilitate final abscission of zoosporangium. Zoosporangia not resistant stages and, if wet, release 8-64 quadriflagellate zoospores (ca. 8 x 3 &m with smooth, isokont flagella ca. 17 &m long) through distinctive pore-papillae. Zoospores form new thalli. Sexual reproduction isogamous. Gametangia ("Kugelsporangien") greatly enlarged terminal, lateral or intercalary cells of prostrate thallus that break through host cuticle and release hundreds of biflagellate gametes through dorsal pore-papillae. Gametes reported to fuse and produce dwarf sporophytes that form abscising meiosporangia that in turn produce quadriflagellate meiospores. Unmated gametes form new thalli. Reported alternation of anisomorphic generations not fully documented; life cycles may differ fundamentally between species.

Information contributed by: R. L. Chapman. The most recent alteration to this page was made on 2024-04-22 by M.D. Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Most recent taxonomic treatment adopted: Thompson, R.H. & Wujek, D.E. (1997). Trentepohliales: Cephaleuros, Phycopeltis and Stomatochroon. Morphology, taxonomy and ecology. pp. x, 149, 60 plates. Enfield & New Hampshire: Science Publishers.

Comments: Circumtropical and subtropical, epi- or endobiotic on leaves, fruits, and young stems of more than 200 species of vascular plant hosts. Species level taxonomy requires revision. Some species may grow intracellularly into host tissue often causing black spots; a nuisance organism on avocado, citrus, and ornamentals. Once considered a pathogen on coffee and tea plants (put possibly only opportunistic following fungal infections). Important studies of the late R. H. Thompson (from which the terminology and much of the basic information in this synopsis is derived) remain unpublished. The basis of host specificity unknown and nutritional relationships between alga and host not well studied.

All motile cells bear flagella with two lateral keels that effectively double the flagellum width in a plane perpendicular to the stroke of the flagella. Both gametes and zoospores with two multilayered structures (MLSs) closely associated with basal bodies. Both lack eyespots, scales and pyrenoids. Gametes with two areas of modifed cell membrane near apical papilla analogous to mating structures in Chlamydomonas. Top layer formed of microtubules extending porteriorly, producing two of four flagellar roots. MLSs similar to, but not necessarily homologous with, MLSs in Charophyceae and lower land plants. Higher plant-like phragmoplast formed in vegetative cell division of C. parasiticus. Although ultrastructural characters suggest affinity to Charophyceae, cladistic analysis of ribosomal RNA sequences supports placement in Ulvophyceae, suggesting early divergence of Trentepohliales in evolution of green algal lineages. Pelicothallos villosa Dilcher from Middle Eocene (ca. 44-52 Ma) only known fossil for Trentepohliales. Thallus preservation and sporangiate branches allows recognition of fossil as Cephaleuros. Sporopollenin in some Trentepohliales may contribute to preservation in more recent geological formations. Similar to Trentepohlia and Phycopeltis, Cephaleuros often lichenized.

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Contributors
Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in CD format. These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above. The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.

Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.

Linking to this page: https://www.algaebase.org/search/genus/detail/?genus_id=43517

Citing AlgaeBase
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 22 April 2024. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 22 November 2024